Cultivar replacement increases water use efficiency in foxtail millet in Shaanxi Province, China.

Cultivar replacement-induced genetic improvement is considered an important factor in enhancing crop grain yield. However, the effect of cultivar replacement of foxtail millet, an important crop in arid and semi-arid regions, on grain yield and drought resistance has rarely been considered. In the present study, we grew five millet cultivars, representative of widely cultivated varieties released from the 1950s to the 2010s in Shaanxi Province, China, in an open rainout shelter (closed during rain events) under two contrasting water treatments (35 ± 5% field water capacity (FWC), and 75 ± 5% FWC) with an aim to detect yield-related parameters, biomass accumulation, water use efficiency (WUE), and plant water-related indices. The millet yield increased with cultivar replacement under normal water conditions, whereas this increase was eliminated under water stress conditions. However, WUE significantly improved under both water conditions over a decade. Correlation analysis indicated that grain yield was significantly affected by biomass, root dry weight at the flowering stage, leaf water potential, whole-plant hydraulic conductivity, root exudation, and leaf gas parameters. WUE had a significant, positive correlation with whole-plant hydraulic conductivity at the jointing stage, whereas it had a significant, negative correlation with root dry weight at harvest. Further, the newly bred cultivar had higher photosynthesis, root exudation, and whole-plant hydraulic conductivity and smaller root dry weight at harvest to hold higher grain yield and WUE. We conclude that future breeding for high-yielding and WUE millet cultivars should focus more on photosynthesis, whole-plant hydraulic conductivity, and root development.